During the development of the nervous system, the temporal and spatial regulation of gene expression is a critical component of neural and glial growth, development, and interactions. These critically timed events are assummed to be a major component in the differential susceptibility of the developing organism to environmental insult.This project examined chemical induced perturbations during development of the NS as indicated by alterations in the spatio-temporal expression of mRNA for various developmentally regulated proteins associated with distinct processes of development. The developmental related effects of chemicals which disrupt thyroid hormone levels are examined to determine specific effects on neuronal and myelin related genes in the development of the nervous system. In addition, thyroid altering agents are examined not only with reference to gene expression during critical periods of development but also in relationship to the development of the neural network as determined both immunohistochemically and Golgi staining. Additional studies are ongoing to determine the role of Il-6 in nervous system development and the adverse effects on the functioning of the nervous system following acute developmental exposure to hyper Il-6.These studies examine the acute toxicity of interleukin 6 on the early post-natal developing CNS and alteration in the normal ontogeny of molecular markers for cortical neuronal network development.